1. Field of the Invention
This invention relates to a circuit capable of providing high speed, high peak power pulses of digitally controlled pulse width using solid state power MOSFET switch modules in conjunction with a high speed pulse transformer.
2. Brief Description of the Prior Art
Travelling wave tubes, which are microwave amplifiers, have generally been powered in the prior art by hydrogen thyratrons. Hydrogen thyratrons are voltage-current switches which, in response to an input pulse, turn on and transfer energy from a storage device, known as a pulse forming network, to a load device, generally a travelling wave tube. A major problem inherent in hydrogen thyratrons is that they have an advertised life of about 300 hours, this seriously affecting the mean time between failures (MTBF) of systems in which they are included. Hydrogen thyratrons also require complex trigger and heater circuits. It is therefore impossible to have a 6.sigma. type of transmitter using a hydrogen thyratron. Furthermore, in order to provide more than one possible magnitude of pulse width, a bank of capacitors is required for each desired pulse width and a high voltage relay and physical switching to the selected capacitor bank is required at the appropriate time to provide the desired pulse width. The capacitors and relays further present reliability problems and tuning of the capacitor banks causes problems in providing the desired spectrum, pulse widths and pulse shapes. Accordingly, both reliability and labor intensity are a problem in the case of hydrogen thyratrons.
In order to alleviate these problems, hard tube modulators have been considered in the past as a substitute. The problem with hard tube modulators is that the voltage of the transmitter is about 38,000 to 40,000 volts and causes emission of a substantial amount of x-rays. Since the device is generally used in airborne radar, the use of heavy lead shielding to shield the x-rays is not a practically available option. There are also other problems inherent in the use of such high voltages. Accordingly, the hard tube modulators are not a practical alternative to the hydrogen thyratron.